The subject matter disclosed herein relates to fuel dispensing systems and, in particular, to heating systems for use in fuel dispensing systems to prevent fuel additives from crystallizing at low temperatures.
Vehicles that use diesel fuels emit large amounts of nitrogen oxides or, more generally, NOx. These emissions are harmful to the environment. Thus, techniques are in place to reduce these emissions. Selective catalytic reduction (SCR) is one technique that converts the NOx into diatomic nitrogen (N2) and water (H2O). SCR utilizes a reductant and a catalyst. Examples of the reductant include anhydrous ammonia, aqueous ammonia, and urea. Various standards and/or government regulations establish the proper solutions for the reductant, which in one form includes an aqueous urea solution, commonly referred to as AUS32 and identified in North America as Diesel Exhaust Fluid and abroad as AdBlue®.
Service stations throughout the world use dispensing systems that store AUS32 to provide regular access for end users that operate diesel-powered vehicles. However, these dispensing systems often encounter problems inherent with the AUS32 fluid. One problem of primary concern is crystallization of the AUS32 fluid. This problem can result in crystal build-up through the components of the dispensing system. The build-up can lead to clogs and other blockages that effectively reduce flow of the AUS32 fluid and, eventually, require maintenance to restore operability of the dispensing system.
Crystallization can occur at low temperatures and, more specifically, at and/or below the freezing point of the AUS32 fluid. The AUS32 fluid will begin to crystallize at about −7° C., forming a slush, and begin to solidify at about −11° C. Unfortunately, many service stations that wish to provide the AUS32 fuel additive are found in locations where temperatures are consistently at or below these critical temperatures for extended periods of time.
Solutions are therefore necessary to prevent crystallization of the AUS32 fluid in these cold environments. One common solution utilizes a large, heated cabinet that encloses the components of the dispensing system. The heated cabinet can maintain the entire dispensing system, or most of the dispensing system, at temperatures that are above the critical temperatures for the AUS32 discussed above. However, use of the heated cabinet, and similar heated compartments, are often considerably larger and/or are sized to heat volumes that are much larger than necessary to maintain the temperature of the AUS32. These features can lead to higher costs of operation (e.g., for the heaters and structure), complicate the refilling process for the end user, and suffer from implementation issues. For example, during a re-filling process, the end user may need to open the cabinet to extract the nozzle and/or to complete the transaction. Once the re-filling process finishes, the end user must then replace the nozzle and close the cabinet. This process relies on the end user to properly close the cabinet door to reestablish the integrity of the cabinet. Unfortunately, situations where the cabinet is not sufficiently closed and/or the cabinet door is left ajar after the re-filling process is complete will defeat the operation of the heated cabinet and can result in freezing of the AUS32 fluid.
Other solutions utilize in-situ heating techniques to elevate and maintain the temperature of the AUS32 fluid. These techniques may utilize a wire, a coil, and/or other element that inserts into the hoses that carry the fuel additive. Energizing these elements injects heat directly into the AUS32 fluid. However, although effective because the elements are in close proximity to the AUS32 fluid, the elements can reduce flow and pressure of the fuel additive in the hoses. Moreover, to afford heating throughout all components that handle the AUS32, and are thus at risk of crystallization, the dispensing system is likely to require different in-situ heating techniques with special designs for the components, e.g., hoses, nozzles, etc. This requirement can add costs and complexity to the design.
Still other solutions attempt to maintain movement of the AUS32 fluid, e.g., when the dispensing system is not in use. These systems deploy intricate fluid systems that allow the AUS32 to circulate continuously, thereby preventing stagnate conditions that can allow crystallization to occur. However, circulating systems also require complicated structure to maintain proper circulation of the AUS32 fluid as well as to avoid leaks and other problems that can lead to effluent from the dispensing system.